Apparatus and method for radiative cooling

ABSTRACT

A system and method for operating a selective emitter is provided. One embodiment comprises a heat sink that absorbs heat from an ambient environment, a heat pipe comprising a cooling portion thermally coupled to the heat sink, a wick portion and a heat dissipation portion, and a selective emitter that is thermally coupled to the cooling portion of the heat pipe. The selective emitter converts absorbed heat into radiative energy that is emitted out through the Earth&#39;s atmosphere.

BACKGROUND OF THE INVENTION

In the arts of refrigeration systems, and in particular radiative cooling systems, a variety of different and complex radiative cooling systems are known that are operable to treat cool an object by radiating energy out through the Earth's atmosphere.

Human activity has caused a build up of CO2 in the earth's atmosphere. CO2 traps heat in the atmosphere. The excess heat is causing damage to the environment. To date all efforts to slow down or stop the accumulation of CO2 have failed. As a result the average temperature of the earth atmosphere has increased by 0.6 C above the average temperature in 1975. However, there are many areas on the planet which have increased by more than 10 C. For example, the arctic is one area of extreme temperature gain.

The atmosphere of the Earth typically absorbs and/or reflects electromagnetic energy (radiation). However, the atmosphere of the Earth has a transparency window in the wavelength range from eight (8) to thirteen (13) μm that coincides with the peak of the blackbody spectrum of typical terrestrial temperatures, around 300K. Silicon based selective emitters, also known as temperature selective emitters, selective thermal emitters, or the like, have been developed to enable the process of radiative cooling. That is, selective emitters perform radiative ejection of heat from Earth to outer space. In practice, a selective emitter cools its non-radiative side below ambient temperature while the radiative side of the selective emitter radiates energy out through the Earth's atmosphere by emitting energy at the wavelength range from 8 to 13 μm. A selective emitter may operate without any external energy.

An example selective emitter cooling system (SERCS, also known as aa Global Cooler) and method is disclosed in U.S. patent application Ser. No. 15/651,595, now published as publication 2018/0023866, which is incorporated by reference herein in its entirety. An example selective emitter is made of layers of silicon nitride (Si₃N₄), silicon (Si), and aluminum (Al) disposed on a base substrate.

Accordingly, there is a need in the arts to remove excess heat in the environment in areas where excess heat is causing the most damage, in both the atmosphere and marine environments.

SUMMARY OF THE INVENTION

Embodiments of the selective emitter radiative cooler provide a system and method for operating a selective emitter. One embodiment comprises a heat sink that absorbs heat from an ambient environment, a heat pipe comprising a cooling portion thermally coupled to the heat sink, a wick portion and a heat dissipation portion, and a selective emitter that is thermally coupled to the cooling portion of the heat pipe. The selective emitter converts absorbed heat into radiative energy that is emitted out through the Earth's atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is an isometric view of an embodiment of a selective emitter radiative cooler.

FIG. 2 is a cross sectional view of an embodiment of a selective emitter radiative cooler.

FIG. 3A is a cross sectional view of an alternative transparent protective cover comprising two panes.

FIG. 3B shows additional features to the protective cover.

FIG. 3C shows additional features to the protective cover embodiment comprised of the two panes.

FIG. 4 is an external view of the complete environmental cooling system comprising a plurality of selective emitter coolers, with optional fans or turbines, and one or more optional flotation device.

FIG. 5 is a cross sectional view of the complete environmental cooling system along the plane A-A′ of FIG. 4.

FIG. 6 is a cross sectional view of the complete environmental cooling system along the plane B-B′ of FIG. 4

DETAILED DESCRIPTION

FIG. 1 is an isometric view of an embodiment of a selective emitter radiative cooler 100. Embodiments of a selective emitter cooler 100 provides a system and method cool heat sinks 102. The heat sinks 102 are remotely coupled to the selective emitter cooler 100 via an intervening flat heat pipe (hybrid vacuum chamber) 104 that transfers heat from the heat sinks 102 to the selective emitter 106. The selective emitter 106 converts the heat received from the flat heat pipe 104 into radiative energy, and outputs radiative energy (radiation) through the Earth's atmosphere. An insulation 108 such as Aerogel or the like, must be attached to the bottom side of the flat heat pipe 104 to force all of the heat being transferred by the flat heat pipe 104 to exit the upper surface of the flat heat pipe 104 and be absorbed by the selective emitter 106. A fluid within the flat heat pipe 104 gets colder as the fluid loses heat as it flows through the portion of the heat sink 102 that is parallel to the surface of the flat heat pipe 104. All insulation used in this invention will be identified as 108 in all drawings to insure clarity. Aerogel insulation is assumed to be sealed to prevent water absorption.

The disclosed selective emitter radiative cooler 100 will become better understood through review of the following detailed description in conjunction with the figures. The detailed description and figures provide merely examples of the various inventions described herein. Those skilled in the art will understand that the disclosed examples may be varied, modified, and altered without departing from the scope of the inventions described herein. Many variations are contemplated for different applications and design considerations: however, for the sake of brevity, each and every contemplated variation is not individually described in the following detailed description.

Throughout the following detailed description, examples of various selective emitter radiative coolers 100 are provided. Related features in the examples may be identical, similar, or dissimilar in different examples. For the sake of brevity, related features will not be redundantly explained in each example. Instead, the use of related feature names will cue the reader that the feature with a related feature name may be similar to the related feature in an example explained previously. Features specific to a given example will be described in that particular example. The reader should understand that a given feature need not be the same or similar to the specific portrayal of a related feature in any given figure or example.

The following definitions apply herein, unless otherwise indicated.

“Substantially” means to be more-or-less conforming to the particular dimension, range, shape, concept, or other aspect modified by the term, such that a feature or component need not conform exactly. For example, a “substantially cylindrical” object means that the object resembles a cylinder, but may have one or more deviations from a true cylinder.

“Comprising,” “including,” and “having” (and conjugations thereof) are used interchangeably to mean including but not necessarily limited to, and are open-ended terms not intended to exclude additional, elements or method steps not expressly recited.

Terms such as “first”, “second”, and “third” are used to distinguish or identify various members of a group, or the like, and are not intended to denote a serial, chronological, or numerical limitation.

“Coupled” means connected, either permanently or releasably, whether directly or indirectly through intervening components.

In an exemplary embodiment, the selective emitter radiative cooler 100 employs a selective emitter 106 to radiate energy upward and out through the Earth's atmosphere. The selective emitter 106 that converts heat into radiated energy (radiation) that is emitted at a wavelength range from at least eight (8) to thirteen (13) μm may be used.

FIG. 2 is a cross sectional view of an embodiment of a selective emitter radiative cooler 100. The selective emitter 106 of an example embodiment has a radiation emitting surface 202 disposed on a substrate 204. The substrate 204 has a lower external surface 206 with the radiation emitting surface 202 disposed on the opposing side of the substrate 204. The radiation emitting surface 202 is defined by layers of various silicon disposed on the substrate 204. The radiation emitting surface 202 is fabricated from layers of silicon nitride (Si₃N₄), silicon (Si), and aluminum (Al) disposed on the substrate 204. In alternative embodiments, any suitable selective emitter that radiates in the 8-13 μm wavelength may be used.

Preferably, the radiation emitting surface 202 is oriented in an upward direction so as to direct the emitted radiation upward and then outward thought the Earth's atmosphere. The external surface 112 of the selective emitter 106 is therefore preferably oriented in a downward orientation.

A transparent protective cover 208 may reside over the selective emitter 106 to protect the radiation emitting surface 202 from weather or other damage, and to thermally isolate the selective emitter 106 from the ambient air temperature. The transparent protective cover 208 is separated from the radiation emitting surface by an air space 210 and supported by supports 212, 108, such as aerogel blocks or other suitable supporting structure. The transparent protective cover 208 may be a crystal, a glass or other suitable covering material. This transparent protective cover 208 is transparent to the radiation that is emitted from the radiation emitting surface 202.

FIG. 3A is a cross sectional view of an alternative transparent protective cover 208 comprising two panes 302, 304. In extremely hot environments a double pane insulative transparent protective cover 208 could be used. The two panes 302, 304 of a transparent protective cover 208 may be separated by aerogel spacers 306 or another suitable spacing means. The space 308 between the two panes of transparent protective cover 208 could be filled with argon gas or the like for additional insulation in hot environments. For applications where maximum insulation is required, the space 308 between the two panes 302, 304 of transparent protective cover 208 could be a vacuum with air proof seals on the edges of two panes 302, 304.

FIG. 3B shows additional features to the protective cover 208. FIG. 3C shows additional features to the protective cover 208 embodiment comprised of the two panes 302, 304. To enhance the transmission of the eight to thirteen (8-13) micron long wave infrared light through the transparent protective cover 208 (or the two panes 302, 304) an antireflection coating 310 on the lower surface of the transparent protective cover 208 (or the panes 302 and 304) could be applied to facilitate the transmission of the 8-13 micron long wave infrared light through the transparent protective cover 208. To block incident light from passing through the transparent protective cover 208, an infrared long pass filter 312 can be optionally used. To make the transparent protective cover water repellent in outdoor environments, a water resistant coating 314, such as titanium dioxide nanoparticles or the like, may be optionally sprayed on or applied to the upper surface of the transparent protective cover 208 (or the pane 302).

When the transparent protective cover 208 (or the selective emitter 106) is tilted slightly, the upper surface of the transparent protective cover 208 (or the two panes 302, 304) will be self-cleaning. Here, rain water flowing across the outside surface of the transparent protective cover 208 (or the pane 302) will wash away accumulated debris.

To minimize thermal warming of the transparent protective cover 208 (or the two panes 302, 304) and the selective emitter 106 from direct sunlight, an optional sunshade 316 illustrated in FIG. 3A may be added to the selective emitter cooler 100. The side of the sunshade 316 facing the sun could have an optional mirror coating 318 to reflect the sunlight to prevent the sunshade 136 from heating up. On the side of sunshade material that faces the selective emitter 106, an optional long wave infrared reflective coating 320 could be applied to the sunshade 316. In addition, an optional titanium dioxide nanoparticle 322 coating could applied to the sunshade 316 to repel water. In tropical environments, the sunshade 316 could be tipped at an angle to shade against the sun which may be vertically overhead during part of the day. The tipping of the sunshade 316 and control of the tilt angle could be automatically controlled in a dynamic manner using a motor and an automatic control system (not shown).

Returning to FIG. 2, the flat heat pipe 104 is defined by a heat dissipation portion 214, a cooling portion 216, and an intervening wick portion 218. A wick 220 extends through the interior of the flat heat pipe 104. A working fluid 222 resides within the flat heat pipe 104. Any suitable working fluid, such as, but not limited to, ammonia with a working temperature range of −65 C to 100 C, or acetone with a working temperature range of −50 C to 100 C, may be used by the various embodiments.

The heat dissipation portion 214 of the flat heat pipe 104 is thermally coupled to (is physically coupled to, so as to be in contact with) the lower external surface 206 of the selective emitter 106 to enable the transfer of thermal energy from the heat dissipation portion 214 of the flat heat pipe 104 up to the lower external surface 206 of the selective emitter 106. Any suitable system or method of physically coupling the heat dissipation portion 214 to the lower external surface 206 of the selective emitter 106 may be used by the various embodiments, including, but not limited to, fasteners, screws, adhesives or the like. In some embodiments, a thermal conductive pad, mat or the like (not shown) may be disposed between the heat dissipation portion 214 of the flat heat pipe 104 and the lower external surface 206 of the selective emitter 106 to facilitate the transfer of thermal energy.

In the various embodiments, the heat that is emitted from the heat dissipation portion 214 of the flat heat pipe 104 is transferred through the lower external surface 206 and into the selective emitter 106. The transferred heat is then absorbed by the radiation emitting surface 202 of the selective emitter 106 for conversion into radiative energy. The generated radiative energy is then emitted as radiation out from the radiation emitting surface 202 into the Earth's atmosphere.

The cooling portion 216 of the flat heat pipe 104 is thermally coupled to (is physically coupled to, so as to be in contact with) the heat sink 102 to enable the transfer of thermal energy from heat sink 102 to the cooling portion 216 of the flat heat pipe 104. In the various embodiments, heat that is absorbed by the heat sink 102 from the surrounding ambient environment is transferred to the cooling portion 216 of the flat heat pipe 104. Any suitable system or method of physically coupling the cooling portion 216 to the heat sink 102 may be used by the various embodiments, including, but not limited to, fasteners, screws, adhesives or the like. In some embodiments, a thermal conductive pad, mat or the like (not shown) may be disposed between the cooling portion 216 and the heat sink 102 to facilitate transfer of heat energy.

Preferably, the internal pressure within the interior of the flat heat pipe 104 is less than atmospheric pressure such that the working fluid 222 in the cooling portion 216 of the flat heat pipe 104 vaporizes at a temperature that is lower than its normal boiling point temperature. During operation, heat is transferred from the heat sink 102 to the cooling portion 216 of the flat heat pipe 104. The heat transferred into the cooling portion 216 causes the working fluid 222 to vaporize as the working fluid 222 absorbs the transferred heat. The warmed vapor (vaporized fluid) then travels up through the wick portion 218 of the heat pipe 104 and then into the heat dissipation portion 214. The vapor then transforms back to its liquid state in the cooling portion 216 of the heat pipe 104, thereby transferring its heat to the heat dissipation portion 214 of the heat pipe 104. The liquid that is formed in the heat dissipation portion 214 of the heat pipe 104 is then wicked back through the wick 220 to be returned to the working fluid 222 that resides in the cooling portion 216 of the heat pipe 104. The wick 220 may be a bundle of fibers or a loosely twisted, braided, or woven cord, tape, or tube, or another suitable porous material that, by capillary attraction, draws the condensed vapor liquid back through the wick portion 218 of the heat pipe 104 to be returned to the working fluid 222.

The heat sink 102 and at least the cooling portion 216 of the heat pipe 104 are optionally enclosed within a pipe-like enclosure 224 having a fluid 226 therein. The enclosure 224 may have any suitable form, such as a tube, duct, trough, channel or the like, such that the fluid 226 is confined to area of the heat sink 102. The cooled fluid can be used for cooling.

In an application with a plurality of adjacent and aligned selective emitter coolers 100, after the fluid 226 has passed through the heat sink 102 on one selective emitter radiative cooler 100, the tube or duct 224 directs the fluid 226 to the next set of heat sinks 104 on the next selective emitter cooler 100 that is adjacent to and behind the first selective emitter cooler 100. Accordingly, a whole series of selective emitter coolers 100 can be lined one behind the other. As the fluid 226 passed through each set of heat sinks 102, its temperature is further reduced. The cooled fluid 226 may then be optionally pumped or otherwise moved through the enclosure 224 to a location where the cooled fluid 226 may be used for cooling purposes. Any suitable fluid 226 may be used by the various embodiments, including, but not limited to, air, radiator fluid, water or the like. To prevent the leakage of the fluid being cooled 226 into the selective emitter area of the selective emitter cooler 100, the tube or duct 224 may optionally have a hermetical seal 228 to seal to the side of the flat heat pipe 104.

In the example embodiment illustrated in FIG. 1, a single selective emitter 106 was illustrated for convenience. One skilled in the art appreciates that a plurality of selective emitters 106 may be bonded to the heat dissipation portion 214 on the upper surface of the flat heat pipe 104 to create a larger total area of radiation emission surface that is used to radiate heat out through the earth's atmosphere. The heat dissipation portion 214 on the low side of the flat heat pipe 104 is insulated by a piece of Aerogel 108 so that all the heat transferred from the heat sinks 102 is absorbed by the lower surface 206 of the selective emitter 106. Further, a plurality of selective emitter cooler 100 may be arranged together to cooperative transfer large amounts of heat energy out through the Earth's atmosphere.

FIG. 4 is an external view of the complete environmental cooling system 400 comprising a plurality of selective emitter coolers 100, with optional fans or turbines 402, and one or more optional flotation device 404. This view of the environmental cooling system 400 shows that the system utilizes multiple units of the selective emitter cooler 100 mounted or arranged together in a rectangular array 406. The width of this array 406 can be made wider by adding more selective emitter coolers 100 to increase the volume of the fluid 226 (FIG. 2) to be cooled flowing through the plurality of aligned heat sinks 102. The length of the array 406 can be lengthened by adding more selective emitter coolers 100 to provide a greater cooling of the fluid 226 flowing through the array 406. The Cross Sections A-A′ (See FIG. 5) and B-B′ (see FIG. 6) show one embodiment of how multiple selective emitter coolers 100 can be connected to together in complete environmental cooling system 400.

FIG. 5 is a cross sectional view of the complete environmental cooling system 400 along the plane A-A′ of FIG. 4. FIG. 6 is a cross sectional view of the complete environmental cooling system 400 along the plane B-B′ of FIG. 4.

The fluid to be cooled flows directly through the width of the plurality of aligned selective emitter coolers 100 as shown in FIG. 5. The fluid 226 flows in the left end of the complete environmental cooling system 400 and out the right end of the complete environmental cooling system 400 illustrated in FIG. 4. The complete environmental cooling system 400 can be used in many applications as noted herein.

In some embodiments, a tube or duct 502 is used for channeling fluid that is to be cooled to be passed to the heat sinks 102. An external case 504 may enclose and secure the plurality of selective emitter coolers 100. An empty space 602 may reside between individual selective emitter coolers 100.

In some applications like marine environments additional pontoons or floatation devices 404 can be attached to the sides of the complete environmental cooling system 400 to float the complete environmental cooling system 400 on the surface of water. In high altitude atmospheric environments helium balloons 404 can be attached the sides of the complete environmental cooling system 400 to elevate the complete environmental cooling system 400 above ground level.

In some applications the fluid 226 to be cooled is stagnant or slow moving, and accordingly, needs to be forced to flow through the heat sinks 102 of the complete environmental cooling system 400. In this application, fans or turbines 402 can be attached to the complete environmental cooling system 400 to induce flow of the fluid 226 through the heat sinks 102. In an example application, the fluid 226 may be ambient air. Here, the fans or turbines 402 circulate the air 226 through the heat sinks 102. The cooled air 226 exits the complete environmental cooling system 400 to return to the ambient environment. In another example application, the fluid 226 may be water, as found in a lake, an ocean, or a sea. Here, the fans or turbines 402 circulate the water 226 through the heat sinks 102. The cooled water 226 exits the complete environmental cooling system 400 to return to the ambient water environment.

The following is a list of possible applications for embodiments of the complete environmental cooling system 400.

a. A complete environmental cooling system 400 installation may be located in high mountain passes to create cooler air that might initiate snow or rainfall in the valleys below.

b. A complete environmental cooling system 400 installation may be located in streams and rivers to help fish that prefer cooler water to thrive.

c. A complete environmental cooling system 400 installation may be located on tethered helium blimps to cool the atmospheric jet stream.

d. A complete environmental cooling system 400 installation may be located on robot ships to cool lakes, bays, and oceans. A benefit of such an installation would be to save fish populations and the fishing industry by providing a cooler habitat.

e. A complete environmental cooling system 400 installation may be located on tethered pontoons in mouths of rivers and/or in major ocean currents to cool water in large areas. Keeping the water temperatures in major ocean currents in their historical temperature ranges will help to maintain the stability of the climate over the entire surface of the planet.

f. A complete environmental cooling system 400 installation may be located on large air conditioner units for office buildings, home, and/or other buildings to reduce heat levels in the building and/or in cities.

g. A complete environmental cooling system 400 installation may be located on heat exchangers for large industrial manufacturing plants, power generating plants, and large ships.

h. A complete environmental cooling system 400 installation may be located next to ice sheets to blow frigid air over ice sheets to slow down or stop the ice from melting.

i. A complete environmental cooling system 400 installation may work in cooperation with weather modeling software to find geographical sensitive areas that have a large impact on the weather patterns. A complete environmental cooling system 400 installation may be located in these sensitive areas to initiate big changes in the weather. This is known as the “Butterfly Effect”.

j. A complete environmental cooling system 400 installation may be located next to an orchard to protect a crop from damage from extreme heat.

k. A complete environmental cooling system 400 installation may be located in the waters of the coast of Australia to cool the water and save the Great Barrier Reef.

l. A complete environmental cooling system 400 installation may be located in a farm pasture to prevent the animals from over-heating.

m. A complete environmental cooling system 400 installation may be located at outdoor music concerts, in back yards, or other areas to keep people from over-heating.

n. A complete environmental cooling system 400 installation may be located in city parks to provide a cool place for people who don't have access to air conditioning.

o. A complete environmental cooling system 400 installation may be located on the streets of large cities to reduce the ambient temperature during the summer.

p. A complete environmental cooling system 400 installation could be connected with a thermal siphon to cool the deep ocean which is storing a lot of heat from global warming.

q. A complete environmental cooling system 400 installation may be located on boats to cool the water in the path of a hurricane to reduce the amount of thermal energy the hurricane can utilize to gain strength and become more destructive.

r. Large numbers of the complete environmental cooling system 400 installation may be located in the Arctic and Antarctic to reduce the temperature in those regions. The warming of the arctic regions has been reported to have a major impact on the weather. The warming of the arctic is causing the permafrost to melt which accelerates the release of CO2 that increases the rate of global warming. Also the warming of the arctic regions also adversely affects the animals living in the arctic. The warming of the Antarctic regions accelerate the melting of the vast ice sheets which will cause the sea levels to rise more rapidly.

s. A complete environmental cooling system 400 installation may be located with thermal siphons put cold water under ice sheets in Antarctica to keep the sheets from melting underneath and breaking off in large pieces that will cause the sea levels to rise. These systems could also be used in Greenland and the Arctic

t. A complete environmental cooling system 400 installation may be located in planes or blimps over forest fires to cool the air that will help the fire fighters to put out the fire faster. If enough cooling in the clouds is created over the fire it might be possible to induce rainfall that would help put out the fire.

u. A complete environmental cooling system 400 installation may be located on the top of the glaciers on Greenland with cooled air to slow down the melting. If all the ice on Greenland melted the sea level could potentially rise 20 feet.

It should be emphasized that the above-described embodiments of the selective emitter radiative cooler 100 are merely possible examples of implementations of the invention. Many variations and modifications may be made to the above-described embodiments. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Furthermore, the disclosure above encompasses multiple distinct inventions with independent utility. While each of these inventions has been disclosed in a particular form, the specific embodiments disclosed and illustrated above are not to be considered in a limiting sense as numerous variations are possible. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed above and inherent to those skilled in the art pertaining to such inventions. Where the disclosure or subsequently filed claims recite “a” element, “a first” element, or any such equivalent term, the disclosure or claims should be understood to incorporate one or more such elements, neither requiring nor excluding two or more such elements.

Applicant(s) reserves the right to submit claims directed to combinations and subcombinations of the disclosed inventions that are believed to be novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of those claims or presentation of new claims in the present application or in a related application. Such amended or new claims, whether they are directed to the same invention or a different invention and whether they are different, broader, narrower or equal in scope to the original claims, are to be considered within the subject matter of the inventions described herein. 

Therefore, having thus described the invention, at least the following is claimed:
 1. A selective emitter radiative cooler, comprising: a heat sink that absorbs heat from an ambient environment; a heat pipe comprising: a cooling portion; a wick portion; and a heat dissipation portion, wherein the cooling portion is thermally coupled to the heat sink; a selective emitter that converts absorbed heat into radiative energy that is emitted out through an atmosphere of the Earth, comprising: a substrate defined by a radiation emitting surface that emits the radiative energy and an opposing external surface that is thermally coupled to the cooling portion of the heat pipe, wherein heat that is absorbed at the cooling portion of the heat pipe from the heat sink is transferred to the heat dissipation portion of the heat pipe via the intervening wick portion, and wherein the transferred heat is absorbed by the selective emitter from the heat dissipation portion of the heat pipe so that the absorbed heat is converted into the radiative energy.
 2. The selective emitter radiative cooler of claim 1, wherein an orientation of the intervening wick portion of the heat pipe is perpendicular to an orientation of the radiation emitting surface of the selective emitter.
 3. The selective emitter radiative cooler of claim 1, wherein an orientation of the intervening wick portion of the heat pipe is substantially horizontal to an orientation of the radiation emitting surface of the selective emitter.
 4. The selective emitter radiative cooler of claim 1, wherein an orientation of the intervening wick portion of the heat pipe is at a predefined angle to an orientation of the radiation emitting surface of the selective emitter.
 5. The selective emitter radiative cooler of claim 1, wherein an orientation of the radiation emitting surface of the selective emitter is substantially horizontal with respect to the Earth's surface.
 6. The selective emitter radiative cooler of claim 1, wherein a wavelength of the emitted radiative energy is within a wavelength range from eight to thirteen μm.
 7. The selective emitter radiative cooler of claim 1, further comprising: an enclosure that encloses at least the heat sink and the cooling portion of the heat pipe, wherein a fluid residing in the enclosure is cooled as the cooling portion of the heat pipe absorbs heat.
 8. The selective emitter radiative cooler of claim 7, wherein the cooled fluid is pumped from proximity to the heat sink to a location wherein the cooled fluid is used for cooling purposes.
 9. The selective emitter radiative cooler of claim 7, further comprising a plurality of selective emitters, where the external surface of each of the plurality of selective emitters is thermally coupled to the heat dissipation portion of the heat pipe.
 10. A method of operating a selective emitter that comprises a substrate defined by a radiation emitting surface that emits the radiative energy and an opposing external surface, the method comprising: absorbing heat using a heat sink that absorbs heat from an ambient environment; transferring the absorbed heat through a heat pipe, the heat pipe comprising: a cooling portion; a wick portion; and a heat dissipation portion, wherein the cooling portion is thermally coupled to the heat sink such that the heat is absorbed from the heat sink by the cooling portion of the heat pipe; transferring the absorbed heat from the cooling portion to a heat dissipation portion of the heat pipe via the intervening wick portion; transferring the absorbed heat from the heat dissipation portion of the heat pipe to the opposing external surface of the selective emitter that is thermally coupled to the heat dissipation portion; converting the transferred heat received by the selective emitter into radiative energy; and emitting the radiative energy from the radiation emitting surface of the selective emitter out through an atmosphere of the Earth.
 11. The method of claim 10, wherein an orientation of the intervening wick portion of the heat pipe is perpendicular to an orientation of the radiation emitting surface of the selective emitter.
 12. The method of claim 10, wherein an orientation of the intervening wick portion of the heat pipe is substantially horizontal to an orientation of the radiation emitting surface of the selective emitter.
 13. The method of claim 10, wherein an orientation of the intervening wick portion of the heat pipe is at a predefined angle to an orientation of the radiation emitting surface of the selective emitter.
 14. The method of claim 10, wherein an orientation of the radiation emitting surface of the selective emitter is substantially horizontal with respect to the Earth's surface.
 15. The method of claim 10, wherein a wavelength of the emitted radiative energy is within a wavelength range from eight to thirteen μm.
 16. The method of claim 10, further comprising: cooling a fluid residing an enclosure that encloses at least the heat sink and the cooling portion of the heat pipe.
 17. The method of claim 16, further comprising: pumping the cooled fluid from proximity to the heat sink to a location wherein the cooled fluid is used for cooling purposes. 